1. Field of the Invention
The present invention relates to an abnormality detecting apparatus for a stepped type automatic speed changer.
2. Description of the Related Art
A conventional abnormality detecting apparatus for an automatic speed changer will now be described with reference to a drawing. FIG. 8 is a view showing a structure of the conventional abnormality detecting apparatus for an automatic speed changer.
In FIG. 8, reference numeral 1 denotes an engine, numeral 2 denotes a torque converter, numeral 3 denotes an input shaft rpm sensor, numeral 4 denotes an automatic speed changer, numeral 5 denotes an output shaft rpm sensor and numeral 6 denotes a readout unit. Numeral 10 denotes a control unit (abnormality detecting apparatus for the automatic speed changer), numeral 11 denotes an input shaft rpm detecting means, numeral 12 denotes an output shaft rpm detecting means, numeral 13 denotes a breakdown detection controlling means, numeral 14 denotes a breakdown information storage controlling means, numeral 15 denotes a speed change controlling means for controlling the automatic speed changer 4 and numeral 16 denotes a learn controlling means for optimizing an rpm change at the time of controlling the speed change.
The operation of the conventional abnormality detecting apparatus for the automatic speed changer will now be described with reference to the drawing.
In general, in the automatic speed changer, the speed change is effected by means of constituents of an internal clutch. However, in the case where the clutch is kept in an abnormal condition and the coupling of the constituents is incomplete, there is a fear that the clutch would be damaged by frictional heat or the like or the automatic speed changer as a whole would be damaged due to the coupling condition that is different from the normal condition.
Accordingly, in general, in the automatic speed changer, the abnormality detection of the speed change condition is effected. As shown in FIG. 8, the abnormal detection is effected on the basis of information on an input shaft rpm speed, i.e., NT of the automatic speed changer 4 and an output shaft rpm speed, i.e., NO thereof.
That is, it is possible for the breakdown detection controlling means 13 of the control unit 10 to calculate a theoretical NT by multiplying the NO by the current gear ratio. This theoretical NT and the detected NT at the same time are compared with each other so that it is possible to judge that the condition is normal in the case where the NTs are the same or close to each other whereas it is possible to judge that the condition is abnormal in the case where there is a difference in rpm exceeding a predetermined level.
Then, the breakdown detection controlling means 13 recognizes this abnormal condition as a breakdown that is out of a speed change synchronism and at the same time records it onto the breakdown information storage means 14. After the breakdown is recognized, the speed change controlling means 15 of the control unit 10 causes the speed change control to stop and fixes the system to a speed change step that is a fail safe condition of the automatic speed changer 4.
In the above-described conventional abnormality detecting apparatus for the automatic speed changer, means which can make a decision only after it is actually brought into the breakdown condition is used. For this reason, when the control unit 10 recognizes an abnormality, the automatic speed changer 4 has already been in the breakdown condition and can not perform the speed change operation. Accordingly, there is a problem that the drivability is deteriorated for the user.
Also, in the case where the abnormality of the automatic speed changer 4 gradually develops, even if a periodical inspection is positively performed by using a repair and inspection method of current general standards, there is a problem that it is difficult to detect the abnormal condition.